1. a Department of Prosthodontics, School of Stomatology, Fourth Military Medical University, 145 Changle West Street, Xi'an, Shaanxi 710032, China
2. b Department of Prosthodontics, School of Stomatology, Fourth Military Medical University, 145 Changle West Street, Xi'an, Shaanxi 710032, China
3. c Department of Environmental Science and Engineering, Xi'an Jiaotong University, 28 Xianning West Street, Xi'an, Shaanxi 710049, China
4. d Department of Prosthodontics, School of Stomatology, Fourth Military Medical University, 145 Changle West Street, Xi'an, Shaanxi 710032, China
5. e Department of Prosthodontics, School of Stomatology, Fourth Military Medical University, 145 Changle West Street, Xi'an, Shaanxi 710032, China
6. f Department of Prosthodontics, School of Stomatology, Fourth Military Medical University, 145 Changle West Street, Xi'an, Shaanxi 710032, China